1. Field of the Invention
The present invention relates to a multicast packet transfer apparatus for receiving and transferring a multicast packet, a multicast packet transfer system and a computer-readable storage medium used in the multicast packet transfer apparatus.
2. Description of the Related Art
Conventionally, when a multicast packet is transferred to another address in a state of original packet data being held, the multicast packet is encapsulated to have a new header added to the header and data of the multicast packet, as shown in FIG. 1.
Such transfer of a multicast packet is described, for example, in “Ip Encapsulation within IP” by C. Perkins, (IETF RFC2003, Oct., 1996). However, when the packet is encapsulated as described above, the packet becomes longer by the length of a newly added header. Therefore, there is a problem that the packet becomes longer than the MTU of the media so that there is a possibility that the packet is fragmentized or divided.
In conjunction with the above description, a transfer system in a loop network system is disclosed in Japanese Laid Open Patent Application (JP-A-Showa 62-56047). In this reference, a reception address of a packet is divided into sub-addresses for a plurality of nodes, and each of the sub-addresses can be allocated with one of set and reset states. A packet transmission source node sets the sub-addresses for destination to the set state and the other sub-addresses to the reset state. After the sub-addresses in the set state are stored, a packet transmission is carried out. Each node transfers the received packet with no change when the sub-address of the received packet for the self node is in the reset state. Also, the node takes the received packet therein when the sub-address of the received packet for the self node is in the set state, and then outputs the packet after setting the sub-address of the received packet to the reset state. Thus, the node determines that data of the packet has been already received, when the packet travels on the loop and is received again.
Also, a packet transfer apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 9-252319). In this reference, when a multicast setting to a plurality of specific terminals is carried out in a lower layer, an address management section (103) generates an upper layer address corresponding to a lower layer multicast address and stores the upper layer address and the lower layer multicast addresses in an address table of a transfer control section (101). When receiving an upper multicast packet, the transfer control section (101) searches the address table for lower layer multicast addresses corresponding to the upper layer address and carries out multicast transmission to the specific terminals corresponding to the searched lower layer multicast addresses through a multicast communication interface section (102).
Also, a data unit which receives and distributes data packets from and to a packet switching circuit and a switching apparatus containing the data unit is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-93589). In this reference, a packet registration section (146) has reception queues (RQ0 to RQ63) corresponding to destinations of reception packets. The packet registration section (146) produces an entry corresponding to the packet in one reception queue (RQ) corresponding to the packet destination at the time of the packet reception. A multicast handling section (148) produces an entry corresponding to the packet in each reception queue of the packet registration means (146) corresponding to each destination in case of that the reception packet is a multicast packet having equal to or more than 2 destinations. A data unit contains a packet output section (150) which reads the packets in the order of production of the entries from the reception queues of a memory (24), to output to a packet switching circuit. An ATM switching apparatus uses the data unit, and a self routing switching device uses the ATM switching apparatus.
Also, a cell copy apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-190663). In this reference, a cell copy apparatus is used for an ATM switching and transmitting apparatus which transfers cells for a unicast call and multicast call, and copies the cell for a copy number contained in control data of the cell when the received cell is for the multicast call. The cell copy apparatus is composed of a unicast call buffer which temporarily stores a plurality of unicast cells, and a multicast call buffer temporarily stores a plurality of multicast call cells. A copy number extraction section extracts the number of copies from the control data of the received cell. A write control unit writes a cell in the unicast call buffer when the received cell is the unicast call cell, and writes the cell in the multicast call buffer when the received cell is the multicast call cell. A load observation control unit observes the load relating to the reception of the cells to determine input load. A read control unit reads out a cell selectively from the unicast call buffer or the multicast call buffer in accordance with the input load by the said load observation control unit. The delay of the unicast call cell can be reduced even if the spacing of the multicast call cell is carried out